Process and apparatus for separating particles of different magnetic susceptibilities

Abstract

A process and an apparatus for separating particles according to the strength of their magnetic susceptibilities includes a mass of loose particles transported on a moving surface over a plurality of long, thin, magnets separated by thin straps of ferromagnetic metal. The magnets are arranged such that the polarities of two adjacent magnets engaging opposite sides of the same ferromagnetic strap are identical. Particles are separated on the moving surface and when that surface passes around a horizontal axis, the particles fall off the surface into selected areas according to the magnetic susceptibilities of the particles. Cooling air flows between the moving surface and magnets to enhance operation and the useful life of the magnets.

What is claimed as new and what it is desired to secure by Letters Patent of the United States is: 
     
       1. An apparatus for magnetic separation of particles comprising a moving bed over which a thin volume of loose particles is transported through a magnetic field, a cylindrical arrangement of rare earth magnets generates said magnetic field to effect a separation between less magnetically attracted particles from more magnetically attracted particles; the improvement which comprises: (a) said cylindrical arrangement of rare earth magnets being formed by a plurality of closely positioned parallel strings of magnets extending lengthwise in a direction generally transverse to the direction of movement of said loose particles on said bed, and wherein each said string of magnets has its two longitudinal sides magnetized with opposite polarities said sides being substantially planar and distanced apart to provide each said string of magnets with a substantial width;   (b) a plurality of central thin ferromagnetic strips each magnetized to its saturation amount and being respectively sandwiched between adjacent said strings of magnets, said strips being substantially thinner than said width of said string of magnets;   (c) each of said strings of magnets being supported on a non-magnetically attractive frame;   (d) said strings of magnets geing arranged such that the polarity of the sides of two said strings touching a single ferromagnetic strip is idnetical; and   (e) means for circulating cooling air between said moving bed and said rare earth magnets.   
     
     
       2. The apparatus of claim 1 wherein each said ferromagnetic strip is magnetized to a value of about 2 tesla. 
     
     
       3. The apparatus of claim 1 wherein said ferromagnetic strip is a low carbon steel having a carbon content of less than 0.15%. 
     
     
       4. The apparatus of claim 1 wherein said rare earth magnets are alloys of samarium or neodymium with iron. 
     
     
       5. The apparatus of claim 4 wherein said alloy is neodymium/boron/iron. 
     
     
       6. The apparatus of claim 4 wherein said alloy is samarium/iron/cobalt. 
     
     
       7. The apparatus of claim 1 wherein said moving bed is a thin-walled rotating shell of non-ferromagnetic material spaced about 0.0012 mm from adjacent surfaces of said rare earth magnets. 
     
     
       8. The apparatus of claim 7 wherein said thin-walled shell is made of stainless steel. 
     
     
       9. The apparatus of claim 7 wherein said thin-walled shell is made of carbon fiber. 
     
     
       10. A continuous process for separating particles according to the strength of their magnetic attractiveness, which comprises feeding a thin bed of loose particles having different degrees of magnetic attraction onto a moving surface under which is a stationary arrangement of magnets producing a high magnetic flux density capable of producing a large coercive force on said bed of particles, said magnets being oriented with the polar axis of each magnet being generally parallel to the direction of travel of said moving surface, said feeding including passing said bed of particles through said magnetic flux which said moving surface travels in a convexly curving downward path with said particles falling from said moving surface at different locations depending on the magnetic strength of each particle to cling to said surface; and allowing said falling particles to be separated by means of one or more splitters positioned selectively to divide particles of less magnetic strength from those of greater magnetic strength said moving surface being spaced about 0.0012 mm from adjacent surfaces of said magnets; said magnets being arranged in parallel lengths with ferromagnetic thin strips being touchingly sandwiched between adjacent said parallel magnet lengths; each said length having two long parallel sides of opposite magnetic polarities and said sides being substantially greater than said thin thickness of each said strip, said ferromagnetic thin strip being about 4 mm in thickness to readily become saturated magnetically by adjacent said magnets without magnetic flux leakage between said magnets, the polarity of adjacent sides of two adjacent said lengths touching opposite sides of the same ferromagnetic thin strip being the same. 
     
     
       11. The process of claim 10 wherein each said magnet is a long slender strip having a length substantially as long as the width of said moving surface measured perpendicular to the direction of movement of said surface. 
     
     
       12. The process of claim 10 wherein said moving surface is non-magnetically attractive. 
     
     
       13. The process of claim 10 further comprising passing cooling air between said moving surface and said magnets to maintain said magnets below about 150° F. 
     
     
       14. A continuous process for separating particles according to the strength of their magnetic attractiveness, which comprises feeding a thin bed of loose particles having different degrees of magnetic attraction onto a moving surface under which is a stationary arrangement of magnets producing a high magnetic flux density capable of producing a large coercive force on said bed of particles, said magnets being oriented with the polar axis of each magnet being generally parallel to the direction of travel of said moving surface, said feeding including passing said bed of particles through said magnetic flux which said moving surface travels in a convexly curving downward path with said particles falling from said moving surface at different locations depending on the magnetic strength of each particle to cling to said surface; and allowing said falling particles to be separated by means of one or more splitters positioned selectively to divide particles of less magnetic strength from those of greater magnetic strength said moving surface being spaced about 0.0012 mm from adjacent surfaces of said magnets; said magnets being arranged in parallel lengths with ferromagnetic thin strips being touchingly sandwiched between adjacent said parallel magnet lengths; each said length having two long parallel sides of opposite magnetic polarities and said sides being substantially greater than said thin thickness of each said strip, the polarity of adjacent sides of two adjacent said lengths touching opposite sides of the same ferromagnetic thin strip being the same, passing cooling air between said moving surface and said magnets to maintain said magnets below about 150 degrees F.